1. Field of the Invention
The present invention relates generally to a downlink packet communication method in a code division multiple access (hereinafter referred to as “CDMA”) mobile communication system employing high speed downlink packet access (hereinafter referred to as “HSDPA”), and in particular, to a method for assigning power of a high speed physical downlink shared channel (hereinafter referred to as “HS-PDSCH”).
2. Description of the Related Art
The mobile communication system has evolved from an early circuit-based mobile communication system, chiefly supporting a voice service, into a high-speed, high-quality packet-based mobile communication system supporting a data service and a multimedia service. A 3rd generation mobile communication system is divided into an asynchronous 3GPP (3rd Generation Partnership Project) system and a synchronous 3GPP2 (3rd Generation Partnership Project 2) system, and standardization for the 3rd generation mobile communication system is currently being conducted for a high-speed, high-quality radio packet data service. For example, standardization for HSDPA is being conducted in 3GPP, while standardization for 1×EV-DV (Evolution-Data and Voice) is being carried out in 3GPP2. The standardization is being performed to find a solution for providing a high-speed, high-quality radio packet data service of 2 Mbps or higher in a 3rd generation mobile communication system. A 4th generation mobile communication system is attempting to provide a high-speed, high-quality multimedia service of a much higher data rate.
FIG. 1 schematically illustrates a cell provided in an asynchronous CDMA mobile communication system. Referring to FIG. 1, a Node B 101 communicates with user equipments (UEs) 104, 106, and 108 over downlink and uplink channels set up therebetween. Downlink physical channels used in HSDPA are divided into a dedicated physical channel, which is exclusively used by one UE and common channels, such as a common pilot channel (CPICH), a primary common control channel (P-CCCH), a secondary common control channel (S-CCCH), a high speed physical downlink shared channel (HS-PDSCH), and a high speed shared control channel (HS-SCCH).
The Node B 101 transmits the above-stated downlink physical channels. In FIG. 1, reference numerals 103, 105, 107, and 109 represent the downlink physical channels with arrows according to their types. Of the reference numerals, reference numeral 103 represents common channels, such as a common pilot channel, a primary common control channel, a secondary common control channel, and other indication channels. The Node B 101 assigns power so that signals on the common channels can arrive at up to a boundary of the cell, and then transmits the common channel signals to the UEs 104, 106, and 108 at the assigned power. This is because all UEs exiting in the cell should be able to receive the common channels. The common channels to which power was assigned the by the Node B is scarcely changed with the passage of time.
Reference numerals 105 and 107 represent dedicated physical channels among the downlink physical channels. An arrow shown by the reference numeral 105 represents a dedicated physical channel for communication with the UE 104, while an arrow shown by reference numeral 107 represents a dedicated physical channel for communication with the UE 106. The dedicated physical channel is assigned optimum power so that only the UE in communication can receive the dedicated physical channel. Therefore, as illustrated in FIG. 1, the UE 106 located at a relatively farther distance from the Node B 101 as compared with the UE 104 should be assigned higher power for its dedicated physical channel. The dedicated physical channels continuously undergo power control. As the dedicated physical channels are simply created or released, transmission power assigned to the dedicated physical channels are changed with the passage of time.
The UE 108 represents a UE receiving an HSDPA service. In FIG. 1, reference numeral 109 denotes a high speed physical downlink shared channel or a high speed shared control channel. The UE 108 receives the high speed physical downlink shared channel or high speed shared control channel 109. Even in the high speed physical downlink shared channel, as the number of UEs or a required service may undergo a change with the passage of time, transmission power assigned thereto is changed.
For these reasons, Node B 101 assigns the total power for a dedicated physical channel and HSDPA within the range of remaining power minus the power assigned to the common channel from the total available transmission power. The assigned total HSDPA power is determined by a controlling RNC (Radio Network Controller, hereinafter referred to as “CRNC”) according to circumstances. The CRNC changes the total HSDPA power according to a change in conditions. The CRNC can inform a Node B of the time-varying total HSDPA power through a Physical Shared Channel Reconfiguration Request message, i.e., an NBAP (Node B Application Part) message. The NBAP message represents the total HSDPA power with an information element (hereinafter referred to as “IE”) called “HS-PDSCH and HS-SCCH Total Power.”
FIG. 2 is a graph illustrating a time-varying ratio of a total transmission power used by the Node B 101. In FIG. 2, a horizontal axis shown by reference numeral 201 indicates a change in time, and a vertical axis shown by reference numeral 202 indicates power assigned to channels in a Node B. A value shown by reference numeral 207 indicates the total transmission power available for the Node B. Reference numeral 203 indicates power assigned to a common pilot channel, and reference numeral 204 indicates power assigned to other common channels such as a primary common control channel and a secondary common control channel. Commonly, the power 203 and the power 204 are scarcely changed with the passage of time. However, a power assignment ratio for the common channels shown by the reference numerals 203 and 204 can undergo a change according to a characteristic of a cell. That is, a ratio of power 203 and 204 assigned to the common channel to the total Node B power 207 can be changed according to a radius of the cell or a geographical environment.
However, Node B power minus the power assigned to the common channel must be assigned for a dedicated physical channel and an HSDPA service. In FIG. 2, reference numeral 205 denotes power assigned to a dedicated physical channel, while reference numeral 206 indicates power assigned for an HSDPA service. The power 205 assigned to the dedicated physical channel is non-periodically changed according to a condition of the Node B, as shown by reference numerals 210, 211, and 212.
FIGS. 3 and 4 illustrate structures of an uplink channel and a downlink channel used for an HSDPA service, respectively. Specifically, FIG. 3 illustrates a structure of a high speed dedicated physical control channel (hereinafter referred to as “HS-DPCCH”), i.e., an uplink channel used for an HSDPA service.
Referring to FIG. 3, an HS-DPCCH includes a plurality of subframes 301. Assuming that one radio frame 302 with a length of 10 ms is comprised of 5 subframes, each subframe has a length of 2 ms. One subframe is comprised of 3 time slots. Of the 3 time slots, a first time slot 303 is assigned for transmission of an ACK/NAK signal for HARQ (Hybrid Automatic Repeat reQuest), and the other 2 time slots 304 are assigned for a channel quality indicator (hereinafter referred to as “CQI”).
The CQI is determined by a UE, and used to indicate quality of the HS-PDSCH. The UE measures a signal-to-interference ratio (hereinafter referred to as “SIR”) of a CPICH, and determines the CQI by estimating an SIR of the HS-PDSCH depending on a ratio of reception power of the CPICH to reception power of the HS-PDSCH. Therefore, the UE must previously have information on the SIR of the CPICH and a ratio of reception power of the CPICH to reception power of the HS-PDSCH, in order to determine the CQI. The SIR of the CPICH can be measured in the UE. The ratio of reception power of the CPICH to reception power of the HS-PDSCH is identical to a ratio of transmission power of the CPICH to transmission power of the HS-PDSCH. Herein, the ratio of reception power of the CPICH to reception power of the HS-PDSCH or the ratio of transmission power of the CPICH to transmission power of the HS-PDSCH will be referred to as an “HS-PDSCH power offset.” For convenience, the term “CPICH power” used herein indicates either transmission power of CPICH or reception power of CPICH, and the term “HS-PDSCH power” indicates either transmission power of HS-PDSCH or reception power of HS-PDSCH. However, it should be noted that when the CPICH power is construed as transmission power of the CPICH, the HS-PDSCH power should also be interpreted as transmission power of HS-PDSCH. The CPICH power has a different value according to a characteristic of a cell. In addition, as shown by reference numeral 206 of FIG. 2, power assigned for HSDPA is also changed with the passage of time. Therefore, the HS-PDSCH power offset is also not a fixed value, but a value changeable according to the type of a cell, timing condition, and power of a common channel.
FIG. 4 illustrates a structure of a downlink channel used for an HSDPA service. In FIG. 4, reference numeral 410 represents a structure of HS-SCCH, and reference numeral 420 represents a structure of HS-PDSCH. In the HS-SCCH 410 and the HS-PDSCH 420, a subframe has a length of 2 ms, and is comprised of 3 time slots. In the HS-PDSCH, transmission of a subframe is started at a time when transmission of a third time slot in the HS-SCCH is started.
As described in conjunction with FIGS. 3 and 4, a UE transmits CQI measured by a CPICH to a Node B over an HS-PDSCH. At this moment, as the CQI is determined by the CPICH, CQI and HS-PDSCH power offset to be applied to HS-PDSCH may be generated. In order to solve this problem, it is necessary to newly define a correct CQI by reflecting an HS-PDSCH power offset in the CQI determined by the CPICH. In addition, the Node B and the UE must previously have information on the HS-PDSCH power offset.
Therefore, it is necessary to newly define a scheme for determining the HS-PDSCH power offset and signal processing procedures for sharing the HS-PDSCH power offset in a mobile communication system.